1. Field of the Invention
The present invention relates generally to a system for performing a warm or hot high-velocity die forging and a method for performing the same. More specifically, the invention relates to the manufacturing of a ring part by a warm or hot die forging, particularly by a forward and backward extrusion, high-velocity die forging.
2. Description of the Prior Art
In recent years, the accuracy of dimensions and shape of die forged parts has been required strictly year by year in order to decrease the number of steps by near net shape forming. On the other hand, the manufacturers have made various attempts to increase the manufacturing efficiency to reduce the costs to make profits.
In order to manufacture various ring parts, a ring part 13 shown in FIG. 4(b) is generally obtained by ring rolling of a ring material 18 shown in FIG. 4(a) after the hot forging.
Referring to the drawings, conventional methods for manufacturing a ring part will be described below.
A method shown in FIGS. 5(a) through 5(d) comprises the steps of: open-up setting a sheared work piece 7 as a first step (FIG. 5(a)); forming a cup-shaped blank by the backward extrusion pressing as a second step (FIG. 5(b)); punching a bottom portion as a dummy portion 10 (which will be hereinafter referred to as a "punched scrap portion") as a third step (FIG. 5(c)); and forming an annular raised portion raised from the circumferentially extending central portion of the inner surface of the work piece by ironing as a fourth step (FIG. 5d)) (this method will be hereinafter referred to as "method A").
Another method shown in FIGS. 6(a) through 6(d) comprises the steps of: open-up setting a work piece 7 as a first step (FIG. 6(a)); forming a cup-shaped blank having a step 11 by the backward extrusion pressing as a second step (FIG. 6(b)); punching a bottom portion serving as a punched scrap portion as a third step (FIG. 6(c)); and forming a ring part by the ring rolling by means of a ring rolling machine shown in FIG. 9 as a fourth step (FIG. 6(d)) (this method will be hereinafter referred to as "method B").
In the case of method A, there is a disadvantage in that, since the central portion of the product is not restricted by the die, ununiform excess thickness may occur in the central portion of the product during the ironing in accordance with the lubrication in the die or the temperature during the forming. Therefore, even if ring rolling is performed, it is difficult to work a ring part as an object of the present invention. On the other hand, in the case of method B, there is a disadvantage in that a ring height 12 may be disengaged from a diesinking portion 19, i.e., a groove portion, of a forming roll during ring rolling to cause defective forming, and there is also a disadvantage in that cracks or flashes may be produced on the line of intersection of the raised inner-surface portion. And the other inner-surface portion since the outside rotating speed is different at the initial stage of forming. Therefore, the aforementioned method B can not be used to work a ring part as an object of the present invention.
In order to eliminate the aforementioned disadvantages in methods A and B, the inventors have studied a method for forming a ring part by ring rolling (which will be hereinafter referred to as "method C"), using the computer aided engineering (CAE) analysis and the plasticine simulation. As shown in FIGS. 7(a) through 7(d), the method C comprises the steps of: open-up setting a work piece 7 as a first step (FIG. 7(a)); preforming a cup-shaped blank by the forward extrusion pressing as a second step (FIG. 7(b)); performed the backward extrusion pressing as a third step (FIG. 7(c)); and punching a punched scrap portion 10 to form a ring part by ring rolling as a fourth step (FIG. 7(d)). In a case where a ring part is forged by the method C, the stroke of the used forging system may be shortened, so that the ring part can be sufficiently formed by means of a high-velocity die forging system having slide strokes per minute of not less than 80 per minute. However, as shown in FIG. 12, the turbulence of metal flow may be produced near the line of intersection of the outer wall portion with the bottom plate portion, or burrs may be produced on the peripheral portion. Since these burrs can not corrected by ring rolling as a secondary processing, it is difficult to stably provide good products.
In order to improve the aforementioned method C, the inventors have studied a method for forming a ring part by the CAE analysis, the plasticine simulation and ring rolling (which will be hereinafter referred to as "method D"). As shown in FIGS. 8(a) through 8(c), the method D comprises the steps of: open-up setting a work piece 7 as a first step (FIG. 8(a)); performed the forward and backward simultaneous extrusion pressing (the double-action pressing) as a second step (FIG. 8(b)); and punching a punched scrap portion 10 to form a ring part by ring rolling as a third step (FIG. 8(c)).
It was found that, in the case of the method D, the forging load can be reduced by 20% in comparison with the aforementioned method C, and it is possible to obtain a smooth metal flow and a sufficiently good quality. However, in order to form a product at higher slide strokes per minute than 80 per minute, a single-action type, short-stroke, die forging system (a horizontal former) must be used. Even if such a system is used, it is not possible to obtain a sufficient filling since the stroke is short, so that it is not possible to form a product by the double action pressing. However, a double-action type, high-velocity, die forging system has not been widely spread. In order to newly provide such a system, infinite costs are required for initial investment, so that such a system can not actually adopted. In addition, even if a long-stroke die forging system is remodeled into a double-action type system, the forging velocity is limited to decrease the manufacturing efficiency, so that the costs of the product are increased. That is, it has been conventionally difficult to obtain a ring blank of a stable quality, which is an object of the present invention.
As mentioned above, in order to form a ring part at higher slide strokes per minute than 80 per minute, a single-action type, short-stroke, die forging system (a horizontal former) must be used. Even if such a system is used, it is not possible to obtain a sufficient filling since the stroke is short, so that it is not possible to form a product by the double action pressing. In addition, a double-action type, high-velocity, die forging system has not been widely diffused. In order to newly provide such a system, costs required for initial investment are increased, so that such a system can not actually adopted.